As the size of semiconductor devices continues to decrease, the stresses which such devices experience increases. For example, the electric current densities experienced by semiconductor devices can be great, particularly in areas in which current flows from one metal interconnect layer to another metal interconnect layer by a small connection referred to as a via.
This increased current density in a localized area such as a via can result in a phenomenon known as electromigration. Electromigration is generally the movement of atoms of a metal interconnect in the direction of current flow. This phenomenon is pronounced in areas with high current density (e.g., such as a via between interconnects).
Thus, in some respects the via acts as a bottleneck for current flow in the semiconductor device. Over time, the atoms which move away from the via due to electromigration will reduce the path through which current can flow near the via, and eventually, enough atoms will move away from the via to cause an open circuit, in which no current will flow from one metal interconnect layer to the next. Thus, electromigration is a serious problem which must be considered when reducing the size of semiconductor devices.
In order to address the problem of electromigration, one method used to construct semiconductor devices includes doping the entire metal interconnect layer with metallic dopants in order to prevent movement of the atoms of the metal interconnect layer in the direction of current flow. However, blanket doping of the metal interconnect layer results in an increased resistivity of the interconnect layer, which degrades performance of the semiconductor device. In some cases, blanket doping can increase the resistance of the device up to 20%, which is unacceptable. Thus, other ways to address electromigration are desired.